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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/53987] [SH] Unnecessary zero-extension before cmp/eq Date: Wed, 17 Dec 2014 21:09:00 -0000 [thread overview] Message-ID: <bug-53987-4-Es1f1bSv7R@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-53987-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53987 --- Comment #4 from Oleg Endo <olegendo at gcc dot gnu.org> --- It seems that converting unsigned values to signed values, i.e. replacing zero-extensions with sign-extensions and recombining sign-extensions with loads could make sense in general. For example, the following code from CSiBE mpeg2dec-0.3.1/libmpeg2/motion_comp.s contains sequences like: _MC_put_x_8_c: .align 2 .L24: mov.b @r5,r0 sett extu.b r0,r1 mov.b @(1,r5),r0 extu.b r0,r0 addc r1,r0 shar r0 mov.b r0,@r4 sett mov.b @(1,r5),r0 extu.b r0,r3 mov.b @(2,r5),r0 extu.b r0,r1 mov r3,r0 addc r1,r0 shar r0 mov.b r0,@(1,r4) .... Here effectively only 8 bit values are calculated. The zero-extensions can be omitted, since the higher bits do not influence the result of the lowest 8 bits and the higher bits are discarded after the 8 bit stores.
next prev parent reply other threads:[~2014-12-17 21:09 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-07-16 23:50 [Bug target/53987] New: " olegendo at gcc dot gnu.org 2012-08-31 18:14 ` [Bug target/53987] " olegendo at gcc dot gnu.org 2013-10-29 21:58 ` olegendo at gcc dot gnu.org 2013-12-16 19:07 ` olegendo at gcc dot gnu.org 2014-12-17 21:09 ` olegendo at gcc dot gnu.org [this message] 2014-12-21 16:54 ` [Bug target/53987] [SH] Unnecessary zero-extensions olegendo at gcc dot gnu.org 2014-12-22 22:27 ` olegendo at gcc dot gnu.org 2014-12-25 1:11 ` olegendo at gcc dot gnu.org 2014-12-30 17:26 ` olegendo at gcc dot gnu.org 2015-01-15 1:37 ` olegendo at gcc dot gnu.org 2015-01-24 13:06 ` olegendo at gcc dot gnu.org 2015-01-27 23:08 ` olegendo at gcc dot gnu.org 2015-08-01 9:57 ` olegendo at gcc dot gnu.org 2015-09-09 12:15 ` olegendo at gcc dot gnu.org
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